To begin, grind the almonds and powdered sugar in a food processor until finely ground and a uniform mixture is achieved. Set aside. Whip the egg whites until foamy, then continue whipping while slowly adding the granulated sugar.Whip until the mixture is stiff, like shaving cream. Add food coloring until desired color is achieved, then carefully fold the meringue the almond-powdered sugar mixture in fewer than 50 strokes, taking care to scrape the bottom of the bowl on the strokes.

@Alyson A couple of things that might help - whip your meringue until it looks like shaving cream and doesn't fall at all if you take the whisk attachment and stand it on the counter. Also make sure you age your shells 30-45 minutes so that they develop a skin. Good luck!